Parvathy Prem

Mercury's polar cold traps host water ice deposits that are likely populated with impact‐delivered water via Mercury's exosphere. However, Mercury's near‐sun location experiences an extremely high photodestruction rate that rapidly destroys water with a timescale of only ∼3.5 hr. Here, we use the PLANET direct simulation Monte Carlo (DSMC) code to investigate the fate of water from a single 1 km radius comet impact striking Mercury's North Pole (30 km/s at angle of 60°). We find that the evolving plume separates into four distinct phases: (a) an early plume phase in which ballistic escape and photodestruction reach their peaks, (b) a reentry phase in which water falling back toward the surface forms a self‐shielded shock‐topped atmosphere that migrates across the surface and ballistic loss ceases, (c) a quasi‐steady phase (QSP) in which a self‐shielding dawn atmospheric enhancement forms and drives a tenuous migration of exospheric water to the cold traps with a longitudinal dependence, and finally (d) a late phase in which self‐shielding ends and photodestruction dominates, effectively ending substantial water migration. In this work, we quantify the fates of the arriving water molecules, and describe some of the more important features of this highly unsteady, evolving three‐dimensional atmosphere. We find that 23% of the initial water is photodestroyed, 65% of the water ballistically escapes the system (of which, 79% photodissociates prior to reaching the Hill radius), and 14% ends up in Mercury's cold traps, which is significantly more than the ∼5% that migrates to the Moon's cold traps during an equivalent impact.

Permanently shadowed regions near Mercury's poles are thought to harbor significant deposits of water ice, the origin of which remains to be conclusively determined. One leading hypothesis is that most of the water observed today may have been delivered by a relatively recent, volatile‐rich impact comparable in scale and age to that which formed Hokusai, a prominent, rayed, northern‐hemisphere crater 97 km in diameter. In this work, we model the transport, loss and deposition of water on Mercury in two different scenarios. We first perform a baseline simulation to update older estimates of the efficiency of exospheric transport of water on Mercury, and find that in the optically thin limit, ∼3% of gravitationally bound water released at perihelion from a point source in Hokusai crater (57.7°N, 16.8°E) migrates to polar cold traps, primarily at the nearest pole. In contrast, we find that a volatile‐rich, Hokusai‐scale impact gives rise to a transient, optically thick atmosphere in which lower photolysis rates due to atmospheric self‐shielding allow for ∼31% of gravitationally bound water to be cold‐trapped and more evenly distributed between north and south polar regions. Cold‐trap deposition is largely completed within one solar day, and the total mass of water deposited is within the range estimated to be present at Mercury's poles today. However, simulation results also suggest that in order to emplace deposits that are sufficiently thick to be radar bright, a larger, slower impact than the 17 km diameter, 30 km/s scenario modeled here may be necessary.

An increasing number of missions to the Moon are planned for the future. However, their long-term, cumulative impacts on the lunar environment are unknown. Research indicates that some important scientific discovery potential may be permanently lost, and exploration may become challenging due to effects of large-scale human activities. Motivated by these questions, we develop and present a generalizable systems-theoretic framework, called Sustainability Evaluations for Lunar Environment Exploration, for assessing the effects of human-built systems on the lunar environment. We contribute a scale and rate diagram of natural and anthropogenic processes on the Moon to provide comparative assessment of important processes that can dominate environmental effects and carry implications for human operations. Additionally, we derive metrics using functional-relationship diagrams of engineered systems to identify environmental effects based on exchange of matter, energy, and information. We demonstrate computation of two selected metrics: the area of the blast zone due to lunar landings and the trajectory of disturbed regolith mobilized from the lunar surface. For the cases considered, our results show that modern spacecraft (that may transport humans to the Moon) can have a landing blast zone area that would be 2–5 times larger as compared to the estimated landing blast zone area of the Apollo missions and up to 30 times larger as compared to some robotic missions. Overall, our analyses highlight the urgent need for careful and rigorous consideration of the environmental effects of engineered systems on the Moon and for understanding the important trade-offs that exist in preserving and (potentially irreversibly) altering the lunar environment.

Lunar volatiles provide a potentially pristine record of the history of the Earth–Moon system in terms of both geologic activity and delivery of volatiles from the outer solar system. Efforts to return humans to the Moon present an unprecedented opportunity to determine the origin of volatiles stored in the ice stability regions but also pose a threat to the scientific value of these volatiles and the lunar exosphere because of the irreversible modification that human exploration will have on the polar volatile ecosystem. We outline here a model for using lunar volatile composition measurements to determine constraints on the origin of lunar volatiles. When applied to results returned by future missions, the results can help trace the history of lunar volcanic activity, solar wind surface chemistry, and volatile delivery to the Earth and Moon through impacts of comets, asteroids, and micrometeoroids. Comprehensive measurements of lunar volatile composition, like those that could be collected by NASA’s Volatiles Investigating Polar Exploration Rover mission, are urgently needed before anthropogenic activity permanently compromises the scientific value of lunar volatiles.

The Volatiles Investigating Polar Exploration Rover (VIPER) is a lunar volatiles detection and measurement mission that will land on Mons Mouton near Nobile crater, close to the Moon’s south pole. One of the analytical instruments embedded within the rover is the Mass Spectrometer observing lunar operations (MSolo) instrument. VIPER’s data will ultimately be used to create lunar water resource maps that may enable a sustained presence on the lunar surface. As VIPER navigates several kilometers of terrain, its onboard analytical instrumentation will characterize the presence of volatiles along the traverse path and identify candidate locations for drilling. Upon selection of a drilling site, the rover will position itself and deploy an auguring, percussive drill down to 1 m depth. Upon extraction, regolith cuttings captured by the auger are deposited on the surface, an activity that will initiate the release of any volatile gases that are subsequently detected and quantified by MSolo. MSolo is designed to identify low-molecular-weight volatiles (between m / z 1 and 100) with unit mass resolution. Volatiles of interest include D / H and O18/O16-bearing species, including possible water contained within the lunar regolith. MSolo is a modified commercial off-the-shelf system, meaning the instrument is based on a commercially available unit that has been ruggedized for space applications.

The Planetary Surface Texture Laboratory at the Johns Hopkins University Applied Physics Laboratory is a facility for the study of the photometric and polarization behavior of regolith analogs using an ∼1.5‐m‐radius arc goniometer system. This system characterizes the photometric and polarization response of granular materials (planetary regolith analogs) at various illumination and viewing angles in the principal plane, enabling both forward and backward scattering observations at phase angles as low as 20 ± 5°. A polarimetric camera with linear polarizers at 0°, 45°, 90°, and 135° captures visible‐wavelength images of samples illuminated by semi‐collimated, unpolarized light. Imaging polarimetry and photometric studies are important for their ability to reveal sub‐pixel information about the nature of planetary surfaces, in particular, texture‐related properties such as porosity and roughness. We develop a calibration pipeline for the system and illustrate how the system can be utilized to understand the polarization and photometric response of planetary surface analog materials relevant to a range of airless Solar System bodies. We present an initial case study using a lunar regolith simulant, JSC‐1A, illuminated with broadband white light and observed between phase angles of 20 ± 5° and 120 ± 5°. We find that the radiance reflected from JSC‐1A decreases with increasing phase angle, while the degree of linear polarization increases, consistent with previous studies. This work illustrates the system's potential to enhance the interpretation of data sets such as those from the PolCam instrument on the Danuri lunar orbiter, and astronomical observations of asteroids.

Propulsive lunar landings can generate high-speed dust sprays that may alter landing sites or damage nearby equipment. We use the direct simulation Monte Carlo (DSMC) method to characterize the transport of dust due to rocket plume impingement on the surface of the Moon. First, we simulate the vertical descent of two types of landers: a large lander that is comparable to the Apollo Lunar Module and a mid-size lander that is comparable to the Chang'E-5 lander. The transient properties of the gas and dust are compared from an initial altitude of 15 m to a final altitude of 2 m. Then, we perform steady-state hover simulations to analyze the sensitivity of our findings to the modeled physics in the code. During the landers' descent, certain properties (i.e., the gas dynamic pressure, the eroded particle mass flux, and the maximum dust speed) are higher in magnitude for the larger lander, while other properties (i.e., the location of the peak pressure, the dust spray angle, and the cumulative distribution of the eroded mass) are the same. For both lander cases, 25% of the eroded mass is dispersed in the final 2 m of the descent, while 50% is dispersed in the final 4.7 m. Consistent with prior authors, we find that a one-way gas–dust interaction model leads to higher gas pressures and dust speeds than a two-way coupled model. Our results can be used to improve our overall understanding of plume–surface interactions on the Moon and to inform future modeling efforts related to powered landings.

The blooming of lunar exploration programs calls for a careful evaluation of the impact of anthropogenic activities on the native lunar environment. Propulsion system plumes are known to deposit a trail of contaminants on the lunar surface up to kilometers from the landing zone. The regolith in proximity of the landing point is mechanically stirred by the plume pressure, while dust can be lifted and transported up to a large distance. Besides these macroscopic effects, the simple presence of a lander standing on the surface affects the surrounding environment via significant outgassing. These effects are expected to strongly influence (and can potentially compromise) the success of science missions, including the study of volatile emission and exospheric species.Moreover, the very safety of human exploration missions, scheduled within the Artemis program, requires the numerical characterization of the blast zone generated by the lander exhaust. The experimentally-validated knowledge available to date is based on robotic landers or on the Apollo program. Upscaling this to Starship-scale landers requires the implementation of accurate numerical models, that account for the not-necessarily-rarefied nature of the flow.In this work, we aim to discuss the main challenges associated with the simulation of rarefied gas dynamic processes for lunar exploration and the required numerical tools. We consider selected real-life scenarios including a simulation of the blast region generated by an Apollo-size and a Starship-class lander, the study of outgassing from a prototype astronaut on a scientific instrument placed at a distance, and a gas-dynamic analysis of the recent Peregrine-One lunar mission. For such problems, we highlight the rarefaction regime and investigate the effect of molecular collisions on the overall flow field and on the local species concentration.

The Peregrine Ion Trap Mass Spectrometer (PITMS) was a mass spectrometer designed to measure lunar gases. PITMS flew on the first flight of Astrobotic’s Peregrine lander via the Commercial Lunar Payload Services (CLPS) program in 2024 January. After launch, the lander suffered a propulsion system anomaly that prevented the mission from reaching the Moon, but PITMS collected 80 high-quality spectra while in cislunar space. PITMS observed abundant outgassing products from the Peregrine lander, including water, MON-25 oxidizer from the propulsion system leak, and traces of combustion products. PITMS data help constrain the nature of the propulsion system failure: oxidizer molecular ratios show that the leak released molecules rapidly enough for them to fully dissociate, and the high observed abundances imply that the oxidizer traveled within the lander surfaces rather than jetting into space. The amount of water offgassed by the spacecraft is substantially more than other planetary spacecraft, so the PITMS results suggest that instruments flying in the CLPS paradigm need to consider lander cleanliness. Though not successful in measuring the native lunar exosphere, the PITMS results showcase the capabilities of a mass spectrometer on board a lunar lander, along with lessons in pragmatism and flexibility that would enable such an instrument to ultimately be successful in the CLPS initiative.